Wish I could do the inverted "
R" like the toy store trademark. Yeah, well... Angles
R angles and are universal. There are a certain number of degrees to a circle. There are a couple of exceptions, but usually only to mathemeticians. A right angle or 90 degrees, is a worldwide standard. It is referring to the planet, and any smaller objects, just as much as your tool tip grind.
A cheapo protractor from China will be as accurate as a B&S for tool grinding. They were a couple of bux the last I bought one. If you spot a B&S or Starrett at a good price, grab it. But don't hold up til you can swing the cost. A Mk-1 eyeball is good enough, once you have a grasp of the angles involved.
An example is the 3-4-5 triangle. I don't know the lesser angles but can calculate one if I needed to know. But the right angle is 90 degrees, period. In any language, by any measurement system. Whether it be normal (360) or grads (400) or radians(Pi). The same thing applies to your tooling by any system. You're not shooting the moon here. Just give it some thought.
As far as metric vs imperial, I find imperial easier because I grew up with it. Until it gets down to 1/32 which I can see, and 1/64, which I can't. But today, with many(most) things made elsewhere, metric is the norm. So learn both and then you will have an easier time of it. Can you spot a 5/16 capscrew just by sight. Or is it an 8mm? It doesn't matter until time to thread a hole. Then match the tap to a fastener. There are a few tricks to learn, but metric is easier to learn from scratch.
Bill Hudson